Some databases use timestamp-based multi-version concurrency control (MVCC) to minimize conflicts with regard to simultaneous transactions. With this arrangement, records in the database are (logically) tagged with creation and deletion timestamps that correspond to transactions that created and deleted the record. If a record has not yet been deleted, the deletion timestamp is unset (which can be represented by some special value, such as maximum representable integer value).
A consistent view (or snapshot) on the database is needed to ensure consistent execution of a SQL statement or of a whole transaction. The consistent view is created by taking the current value of a commit timestamp generator (i.e., a timestamp) which is appended or associated to each record. This timestamp is then used against create and delete timestamps (CTS, DTS) to decide visibility of the record.
A record is considered visible if its timestamp (provided the unset/invisible timestamp is defined as maximum representable integer value) when it is less than or equal to the timestamp stored in consistent view (CV).
If the creation timestamp is visible and deletion timestamp is NOT visible, then the record as such is visible.visible(record)=visible(CV,record·CTS)∀−visible(CV,record·DTS)